Although born in Burbank, California, she was discovered by accident while on vacation. When Descher was about five years old, her family had travelled across country to New York City where the girl fell in love with the theater after seeing The Red Shoes ballet on Broadway. On the way home, they stopped at Jackson Hole, Wyoming where coincidentally a film was being shot. The director saw her, and needing a child for the film, approached her parents. However, as they had to return home, they contacted the director later. Within six months, Sandy appeared in her first movie, It Grows on Trees, which was released in 1952.

Next she appeared in a brief, but key role in the classic science-fiction film, Them! (1954). She played a catatonic child whose parents have been killed by gigantic ants. Unable to speak, she can only scream "Them", giving the film its title. The movie's cast included Edmund Gwenn, James Arness and James Whitmore.

Her memories of her acting years are almost all pleasant, except she did receive a number of kidnapping threats. She was even interviewed by the F.B.I. after one obsessed woman stalker became convinced she was her long-lost daughter.